Virtually all motor vehicles (cars, trucks, and the like) produced in recent years are equipped with safety belts that wind onto retractors for storage and are unwound for use. The retractors most often used are emergency locking retractors ("ELR"). The ELR type of retractor has a mechanism that normally allows the belt to be unwound when it is in use so that the vehicle occupant can lean forward but locks automatically in the event of a collision or other emergency that could cause the occupant to be thrown forward. Some ELR's are locked by a mechanism that senses rapid rotational acceleration of the belt reel resulting from sudden pulling out of the belt. Others have a mechanism that is actuated by a device that senses acceleration of the vehicle in any direction resulting, for example, from a collision. Some ELR's have both types of locking mechanisms (belt pull-out responsive and vehicle acceleration responsive).
FIGS. 10A and 10B show in simplified form two common types of acceleration sensing devices used in ELR's of the vehicle acceleration-responsive type. Many specific designs for these two types have been devised.
The type shown in FIG. 10A comprises a case 1, the bottom of which has a concave surface (a cone or a spherical segment, for example) in which an inertial body 2 in the form of a ball rests. A pawl 3 normally resides in an inactive position (solid lines) when the ball 2 is in its stable position in the bottom of the concave surface but pivots upwardly (phantom lines 3') and thereby causes the ELR locking mechanism to be actuated whenever the inertial body rolls or slides generally horizontally along the concave surface in any direction. Examples of devices of the type shown in FIG. 1 are found in: U.S. Pat. No. 4,176,809 (1979); French Publ. Pat. Appln. No. 2,396,558 (1979); West German Publ. Pat. Appln. No. 27 14 340 (1978); and West German Publ. Pat. Appln. No. 27 46 091 (1978).
In the acceleration sensing device shown in FIG. 10B an inertial body 5 rests by means of a stem portion 5a in a recess in the bottom of a case 4. A cam follower projection on a pawl 6 rests in a concave surface 5b on the top of the body 5. In the absence of a high acceleration of the case 4, the body 5 rests stably in an upright position, but when the case 4 is accelerated in any direction, the inertia of the body 5 causes the body 5 to tilt in a direction opposite to the direction of the acceleration, whereupon the pawl is pivoted to the active position shown in the phantom lines 6'. Devices of the type of FIG. 10B are described and shown in U.S. Pat. Nos. 4,018,400 (1977); 4,083,512 (1978), and 4,135,410 (1979).
The reliability of known acceleration sensing devices has been well-established by use in many millions of vehicles. There is, however, a problem that has not been solved--in addition to the intended function of initiating locking of the ELR belt reel upon a generally horizontal acceleration, the known devices can initiate locking of the reel upon a generally vertical downward acceleration of the vehicle, a common occurrence on bumpy roads, for example. When the case (1 or 4) is accelerated downwardly, the inertia of the body (2 or 5) causes it to remain stationary vertically, and because the pivot axis of the pawl (3 or 6) also moves down with the case, the pawl is pivoted upwardly and initiates locking of the reel-locking mechanism. Also, the bouncing up and down of the body (2 or 5) in known devices produces a bothersome noise. Some vehicle occupants can become concerned that something is wrong with the retractor mechanism when they hear something loose bouncing around in it.